Radio locating system for producing stereoscopic indications of objects



Sept 1955 D. E. suNsTElN 2,7l8,00

RADIO LOCATING SYSTEM FOR PRODUCING STEREOSCOPIC INDICATIONS OF OBJECTS Filed Nov. 6, 1946 7 Sheets-Sheet 1 AGE/V75 Sept.. 13, 1955 D. E. sUNsTElN 2,718,000

ARADIO LocATrNG SYSTEM FOR PRonucING STEREOSCOPIC INDICATIONS OF` OBJECTS Filed Nov. 6, 1946 7 Sheets-Sheet 2 za-f A V Sept. 13, 1955 D. E. sUNsTElN 2,713,000

RADIO LOCATING SYSTEM FOR PRODUCING STEREOSCOPIC INDICATIONS OF OBJECTS Filed Nov. 6, 1946 7 Sheets-Sheet 3 IN V EN TOR.

Sept. 13, 1955 D. E. suNsTElN 2,718,000

RADIO LOCATING SYSTEM FOR PRODUCING STEREOSCOPIC INDICATIONS OF' OBJECTS Filed Nov. 6, 1946 7 Sheets-Sheet 4 HQ. f

Sept. 13, 1955 D. E. suNs'rElN 2,713,000 RADIO LCATING SYSTEM FOR PRODUCING STEREOSCOPIC IN DICATIONS OF' OBJECTS 7 Sheets-Sheet 5 Filed Nov. 6, 1946 INVENTOR. /W/ E. 10A/575W AGE/V75 sept. 13,1955

Filed. Nov. 6, 1946 D. E. SUNSTEIN RADIO LOCATING SYSTEM FOR PRODUCING STEREOSCOPIC INDICATIONS OF OBJECTS 7 sheets-smet e lll'lI Cardi/09 3 @Wwf Sept 13, 1955 D. E. suNsrl-:IN 2,7%,000

Y RADIO LOCATING SYSTEM FOR PRODUCING STEREOSCOPIC INDICATIONS 0F OBJECTS Filed Nov. 6, '1946 '7 Sheets-Sheet '7 INVEN TOR.

I lRADIO LOCATING SYSTEM FOR PRODUCING.

STEREOSCOPIC INDICATIONS OF OBJECTS David E. Sunstein, Cynwyd, Pa., asslgnorto Philco Corporation, Philadelphia, Pa., a corporah'on of Pennsylvania Y Application November 6, 1946, Serial No. 708,074

12 claims'. (cl. 34a-7.9)

This invention relates to radiant energy systems in which signals transmitted, retransmitted or reliected from a plurality of target objects variously disposed in space y are-intercepted at a receiver and utilized either directly ample, an orientable antenna which both transmits pulses' o'f high frequency energy and selectively receives reflections of said pulses from different target objects. However the invention is not limited to the use of such a system. A pulse-echo system employing separate transmitting and receiving antennae may be used in which only one antenna (which may be either the transmitter or the receiver) is directionally controllable and the other may be non-directional. Furthermore a continuous wave system, ratherthan one of the pulse-echo type, may be used. Still another alternative, which, for example, might be resorted to when the system is used to track friendly aircraft, consists in providing a multi-directional beacon transmitter in each aircraft and means on the ground for selectively receiving the transmissions therefrom.

In'the most elementary system according to the invention, a stereoscopic presentation is produced correvf-sponding to a virtual viewing point at the location of the directionally controllable antenna (whether this be 'the transmitter or the receiver or both). It may be desirable, under certain circumstances, to translate the virtual view- -ing point of the presentation to some arbitrarily selected this purpose a cathode ray tube or like indicator is generally usedto provide a two-dimensional plot from which certain data with respect to target location can be read more or less directly. It is known to use plots of several different forms, each of which is adapted to emphasize, and to make conveniently available, certain target coordinate data. Thus, for example, the form of presentation commonly referred to as A-Scan provides a plot of reflected signal amplitude versus range. 'Ihe so-called 'B and C scans yield, respectively, plots of range and elevation versus azimuth, while the P. P. L scan provides a polar plot of range versus azimuth angle. While each of these forms is desirable for,'and peculiarly suited to, certain vspecific applications, none of them is suitable for use directly in a system of the sort here contemplated. To obtain a true and undistorted three-dimensional or 4stereoscopic presentation, corresponding to direct visual observation, it is necessary, in effect, to superpose stereo scopically two presentations corresponding respectively to the images which, for example, would be produced by two optical lenses having displaced parallel axes. Thus, in this instance it is necessary to reconstruct, from the data provided, for example by a radar system, indications corresponding to those which, for example, would be produced by appropriately situated cameras and which, for convenience, may be referred to as camera presentations. It is accordingly an object'of the invention to provide methods of and means for obtaining such presentations utilizing the data available, for example, from a conventional radar transmitter and receiver system.

Given means .for converting available data into visual camera presentations, it is then possible, in accordance with the invention, to supply two such means with data from separate and differently located systems to produce separate and differing presentations which, when viewed stereoscopically by suitable means, will convey to the observer a three-dimensional view of objects in space corresponding, at least so'far as the relative positions of the objects are concerned, to that which would be obtained by direct and unimpeded visual observation. This constitutes another object of the invention.

Still another object of the invention is to provide means whereby the two displaced camera presentations needed for the production of a stereoscopic presentation can be produced from data supplied, for example, from a single radar system comprising a transmitter, a receiver 'and an orientable antenna.

As hereinbefore mentioned, the data which is used to -produce the camera presentations can be converted,

. through the application of known methods, to yield a stereoscopic presentation corresponding to a remote virtual viewing point. More specifically, in the instance of data supplied by a ground based system, the'data may be converted to yield a presentatidn related to a virtual viewing point somewhere above the ground. When this is done the difficulty may arise that it will be impossible from the presentation to determine within which of two opposed hcmspheres a given target is actually situated. Hence it is another object of the invention to provide means for eliminating this ambiguity.

Other objects and features of the invention will become apparent from consideration of the following specification with reference to the accompanying drawings in which:

Fig. 1 is a diagram in tridimensional orthogonal coordinates, to which reference will be made in explaining the manner in which azimuth, elevation and range data, with respect to the positions of objects variously disposed lin space, may be converted into bidimensional rectangular coordinate data for providing a bidimensional presentation corresponding to that which would be obtained by visual observation from the reference point in space to which the azimuth and elevation data are referred, or from a point in space displaced in a single coordinate direction from said reference point;

Fig. 2 is a schematic diagram of circuits for converting azimuth and elevation data, referred to a predetermined reference point in space, into bidimensional coordinate data for providing a visible presentation of said data referred to a reference point corresponding to said predetermined reference point in space. The circuits illustrated are suitable for use in the detecting signal generator 26 of the embodiment according to Fig. 3;

Fig. 3 is a block diagram of a complete radar system Patented Sept. 13, 1955 I yoptical image of any point in space.

for providing a stereoscopic presentation indicative of the positions of objects variously disposed in space referred to a reference point corresponding to the physical location of the radar apparatus employed to provide data with respect to the azimuths and elevations of the objects;

Fig. 4 is a schematic diagram of circuits for converting azimuth, elevation and range data, referred to a predetermined reference point in space, into bidimensional coordinate data for providing a visible presentation of said data referred to a predetermined reference point in space displaced in a single coordinate direction from said firstnamed reference point. The circuits illustrated are suitable for use in the deecting signal generator 95 of the embodiment according to Fig. 5;

Fig. 5 is a block diagram of a complete radar system for providing a stereoscopic presentation indicative of the positions of objects variously disposed in space referred to a predetermined reference point displaced in a single coordinate direction from the physical location of the radar apparatus employed to provide data with respect to the azimuths and elevations of the objects;

Fig. 6 is a diagram in tridimensional orthogonal coordinates, to which reference will be made in explaining the manner in which azimuth, elevation and range data, with respect to the positions of objects variously disposed in space, may be converted into bidimensional rectangular coordinate data for providing a bidimensional presentation corersponding to that which would be obtained by visual observation from a predetermined reference point in space displaced in three orthogonal coordinate directions from another reference point in space to which the azimuth and elevation data are referred;

Fig. 7 is aA schematic diagram of circuits for converting azimuth, elevation and range data, referred to a predetermined reference point in space, into bidimensional coordinate data for providing a visible presentation of said data referred to a predetermined reference point in space displaced in three orthogonal coordinate directions from said first-named reference point. The circuits illustrated are suitable for use in the deecting signal generator 173 in the embodiment according to Fig. 8; and

' Fig. 8 is a block diagram of a complete radar system for providing a stereoscopic presentation indicative of the positions of objects variously disposed in space referred to a predetermined reference point in space, which reference point is displaced in three orthogonal coordinate directions from the physical location ofthe radar apparatus employed to provide data with respect to the azimuths and elevations of the objects.

The positionrof a target in space with reference to a predetermined point is conveniently specified in terms of the elevation angle (o), the azimuth angle (0) and the range (r) from the point to the target.' In a conventional radar system employing a scanning antenna, the angles and 0, for a particular target, are directly related to and derivable from the orientation of the antenna structure when it is pointed at the target, as indicated by the fact that a transmitted pulse of high frequency energy is relleced from the target and intercepted by the antenna. Likewise, the range r is a function of the time required for the pulse to travel to the target and return. From the angles and 0, assuming a lens of predetermined focal length (f) located at the predetermined reference point, it is possible to specify the coordinates, in the focal plane of the lens, of the These coordinates are independent lof r inasmuch as all points in space lying on the same straight line through the center of the lens are imaged at the same point in the focal plane. If in rectangular form, the coordinates correspond respectively to the horizontal and vertical deecting potentials which must be applied to. an electrically deected cathode ray tube to produce a camera presentation of the point in .space as would be seen from the aforementioned reference point. A

Referring now to Figure 1it will be apparent that the deliecting signals Ex (horizontal) and Ey (vertical) can be expressed generally in terms of the angles and 0 and the focal length f. 'It may be assumed that a camera presentation is to be produced of an object at point T `such as would be produced by a lens of focal length f located at a reference point O, whose optical axis coincides with the axis Z-Z of the rectangular coordinate system defined by the axis X-X', Y-Y' and Z-Z'. The elevation and azimuth angles of the point T with reference to the coordinate system are designated respectively by qb and 0. The point T is imaged at the point T haxing X and Y coordinates Ex and Ey respectively, which correspond to the desired deecting signals. It can readily be shown that Ex and Ey are completely specified by the following expressions: v

Likewise it will be apparent that the perpendicular. radial displacement r' of the point T from the axis Z--Z is proportional to the cotangent of the elevation angle p and that'the azimuth of point T' di'ers from that of point T by 180.

Data with regard to the variations of and 0 can readily be obtained from any conventional radar, for example, through the employment of self-synchronous motors or other similar means. These data may be utilized in a circuit of the sort shown in Figure 2 to generate the desired deflecting signals according to Expressions 1 and 2 given above. In particular it should be noted-that these deecting signals are independent of the range to point T from point O, and that hence the range data supplied by the radar, in this instance, is not used. Such range data, however, does become useful in other embodiments of the invention as will hereinafter be set forth.

In the circuit arrangement of Figure 2 the potentials impressed between the point and each end of potentiometer 1 by batteries 2 and 3 correspond to the desired focal length (f) of the system. The slider'on the potentiometer is moved in synchronism with the elevation angle p so as to derive a potential whose value is f cot 95.' This may be accomplished either byI varying the displacement of the slider from the 0 Ez=f (cot cos 6) Eu=f (cot sin a) .center point proportionally to cot or by varying its displacement proportionally to 4 and providing, in the potentiometer, a tapered resistive element whose resistance varies throughout each half of its length proportionally to cot 4:. Various methods of constructing such potentiometer resistance elements are well known in the art, for which reason it is deemed unnecessary to discuss their construction in detail here. It will, of course, be appreciated that such variation in displacement or resistance cannot-be achieved throughout the complete range of values of since cot approaches infinity as 4 approaches zero. This, however, does not present a serious problem, its only effect being to limit somewhat the eld of view which can be reproduced in the camera presentation. The same limitation is present, usually to an even greater extent, in an optical camera. However, even this slight limitation can be overcome as will hereinafter be set forth.

The signal takenv from the slider of potentiometer 1 is supplied through connection 4 to a slider 5 of a circular potentiometer 6. Potentiometer 6 is provided with a second slider 7 which may be mechanically (but not electrically) connected to slider 5 so that the two will always make contact with the resistive element at points thereon which are diametrically opposite one from the other.

Sliders 5 and 7 are moved in synchronism with the azimuth angle 0, so that between points 8 and 9 there is developed a signal Ey=f (cot sinA 0), and so that between points 10 and 11 there is developed a signal As already pointed out, these are the required deflecting signals to yield the camera presentation. To achieve this result, as in the case of potentiometer 1, the displacement of sliders 5 and 7 may be varied non-uniformly as a function of the azimuth angle 0. Alternatively the resistance throughout each quadrantal sector of the resistive element may be tapered in such a way as to produce the desired sinusoidal variation as a function of when the sliders are moved at a uniform rate.

In order to provide a stereoscopic presentation in the usual manner, it is necessary to provide two camera presentations corresponding to views of the object T from two different points separated by a distance which may preferably bemade substantially greater than the spacing between the eyes ofthe observer. In this manner it is possible greatly to enhance the stereoscopic effect and thereby to increase the facility wi.h which the observer can distinguish objects differing only slightly in range. Thus, in Figure l, if P is a point displaced from point 0 by the required amount, the required data for producing the two presentations` may be obtained from two separate radar equipments located respectively at points 0 and P. Reference is now made to Figure 3 which shows a complete system for this purpose.

The two radars 20 and 21 are equipped with antennas 22 and 23 constructed and arranged to scan both in elevation and azimuth. Although, as shown, these antennae are of the mechanically orientable type, it would be equally feasible to use, for example, antennae comprising fixed elements, whose directionalities are controllable by varying the phasing of the signals supplied to or received from the several directional elements of each. This statement applies, in fact, to the antennae in all of the systems disclosed herein. Preferably antenna 22 is caused to scan a target area in a predetermined systematic manner and antenna 23 is controlled from radar 20 through connection 24 so as to scan in exactly the same manner (i. e. so that the electrical axes of the two antennas are always parallel). Both radars 20 and 21 preferably transmit pulsesof high frequency energy simultaneously, which may be achieved by controlling radar 21 from radar 20 through connection 24. Elevation and azimuth data (45 and 0) are supplied through connection 25 to a deecting signal generator 26, which may be of the form shown in Figure 2 and which is adapted to provide horizontal and vertical deflecting signals Ex and Ey in accordance with Expressions l and 2. The horizontal deecting signal, Ex, is supplied through connections 27, 28 and 29 to the horizontal deecting plates (not shown) of a pair of electrically deected cathode ray tubes 33 and 34. Likewise the vertical deflecting signal, Ey, is supplied through connections 30, 31 and 32 to the vertical dellecting plates (not shown) of the same cathode ray tubes. The electron beams of the two tubes are thereby caused to scan the screens 35 and 36 of the respective tubes according to the same pattern, as determined by the motion of scanning antennas 22 and 23.

However, it will be-noted that both scanning antennas 22 and 23 will not be directed at the target object T at the same instant of time. Thus when the electrical axis of antenna 22 is directed along line 37 at point T, the electrical axis of antenna 23 will be directed along line 38 which does not intercept point T. At some later time in the scanning cycle antenna 23 will assume the broken line position 23a such that its electrical axis will be directed along line 40 so as to intercept point T while antenna 22 will assume the position, indicated by broken lines 22a, with its electrical `'axis directed along line 39. Thus it will be apparent that reflections of pulses successively transmitted from both antennas '22 and 23 will be reected at different times from target T and will arrive at radars 20 and 21 at correspondingly dierent times. Reflections received by radar 20 are transmitted through connection 41 to control the intensity of the electron beam in cathode ray tube 33. Likewise reiections received by radar 21 are transmitted through connection 42 to control the intensity of the electron beam in cathode ray tube 34. By reason of the fact th' screens of tubes 35 and 36 are scanned in identical ...s` ner by their respective electron beams, the reflection from l0 target T supplied to cathode ray tube 33 will appear at a different point on screen 35 from that at whichl the delayed reflection from target T supplied to tube 34 will appear on screen 36. Thus there will appear on screens 35 and 36 dierent camera presentations of the same target object. Similarly, different camera presentations will appear on screens 35 and 36 for other\targets (not shown) within view of the scanning antennas 22 and Y23. The two different camera presentations may then be presented opiically, for example, through a conventional stereoscopic viewer 43 to the eyes 44 of an observer so as to provide him with a three-dimensionalview of all of the objects within view of the scanning antennas 22 and 23 of radars 20 and 21. V

From study of Figure l, it will be seen that the angles and 0', denoting respectively the elevation and azimuth of point T with reference to point P, can be expressed in terms of the angles and 9. From this it follows that, knowing the variations in and 0, deliecting signals can be derived which may be applied to the horizontal and vertical deflecting plates of a cathode ray tube which,

when its electron beam intensity is controlled by reflections received by a radar located at point 0, is capable of producing a camera presentation corresponding to that which would be produced by a radar located at point P and scanning in the same fashion as the one at point O. Thus a single radar located at point O can supply all of the data required for stereoscopic presentation. The

new horizontal and vertical deliecting signals Ex and EyY above referred to are given by the following expressions:

E,=f cot cos 't9-(Egg) (3) E= f (cot sin o) (4') 4 It will be noted that the vertical deflecting signal is a the same as that applied to the vertical dellecting plates of both tubes in the system of Figure 3. This is owing to the fact that point P is displaced from point Osolely Iin the X direction. If point P were displaced in both X and Y directions, the expression for Ey would be correspondingly modified. Y

Referring now to Figure 4, which illustrates a circuit for generating these deflecting signals, a signal f cot 4 is derived from potentiometer 50 whose slider is 'moved in synchronism with the elevation angle p as in the case of potentiometer 1 of Figure 2. Likewise, as in the case of Figure 2, the signal derived from potentiometer 50 is supplied through connection 51 to slider 52 of poten-v According to Equation 3, there is to be subtracted from this latter signal a signal equal to f(OP :se is) to yield the new horizontal deecting signal for one of the cathode ray tubes. However, it is found more convenient in practice to add to f (cot sin 6) a signal whose value is equal to OP csc f( 21' for the other tube.

to yield the horizontal detlecting signal for one tube, and ,to subtract from f (cot qs sin a signal whose value is equal to (OP csc f 2r Vto yield the horizontal deecting signal for the other tube. The detlecting signals thus produced, together with the vertical deecting signal E=f (cot sin 0), are such as to provide camera presentations corresponding to the views from ,points displaced respectively in opposite di- 'rections by amounts equal to from the actual location of the radar antenna.-

A signal inversely proportional to r, to provide the denominator for the expression 'potentiometer 62. Potentiometer -62 is center-tapped to ground through resistor 63 and its slider is moved in synchron'ism with the elevation angle to yield a signal proportional to To this end the potentiometer slider may be moved at a non-uniform rate over the resistive element, or the resistive element may be appropriately tapered to yield the same result. The signal from potentiometer 62 is supplied to the primary winding of a transformer 64 having connected in series with its secondary winding a series resistive network comprising resistors 65, 66 and 67. Terminal 56 of potentiometer 53 is connected to a center tap on the secondary winding of transformer 64 whereby, with appropriate adjustment of resistor 66, the signals from potentiometers 53 and 62 will be combined to yield, across terminals 68, the desired horizontal deecting `signal E,=f (cot qs cos 19d-(lsu) for one tube and, across terminals 69, the complementary horizontal deecting signal UP csc In the system, as illustrated in Figure 5, employing a single transmitter, receiver and antenna to provide a stereoscopic presentation, the radar 90 and its antenna 91 are located intermediate between the points O and P, the' virtual viewing points for the two diiercnt camera presentations to be produced on screens 35 and 36 of cathode ray tubes 92 and 93 respectively. Azimuth and elevation infomation from radar 90 is supplied through connection 94 to detiecting signal generator 95 which may be of the form just described with reference to Figure 4. The vertical dellecting signal Ey is supplied through `connections 96, 97 and 98 to both tubes 92 and 93, while the horizontal deecting signals Ex and El' are supplied through connections 99 and 100 to tubes 92 and 93 respectively. Rellections from targets received by radar 90 are supplied through connections 101 and 102 to both spective electron beams.

cathode ray tubes to modulate simultaneously their 4ri:-

As in the syste'm of Figure 3, the complementarycamera presentations produced on the screens 103 and 104 of the cathode ray tubes may be translated optically through a suitable stereoscopic viewer 105 to the eyes 106 of an observer to give him the desired three-dimensional impression of the space scanned by antenna 91 of radar 90.

In the immediately foregoing discussion referring to Figures l, 4 and 5, methods and means have been disclosed for translating the virtual viewing point in one coordinate direction with reference to the actual location of the radar transmitter and receiver. In certain applications it may be desirable to translate the virtual viewing point in two or in all three coordinate directions. Thus, in the instance of a ground-based radar located at an airport and used to observe air trac within a predetermined radius which is large compared to the average level of ight, the portion of the presentation corresponding to the average level of ight will tend to become 4 crowded under conditions of dense traic in the vicinity of the field. Moreover, owing to practical limitations in the construction of the cot 4 potentiometers, hereinbefore referred to, it will be impossible to present aircraft ying at low angles of elevation. This diiculty can be overcome by locating the virtual viewing points, of a stereoscopic radar system in accordance with the invention, beneath the surface of the ground. The following description and discussion relates to a stereoscopic system for providing displacement of the virtual viewing point in X, Y and Z directions in a rectangular coordinate system. Referring now to Figure 6, let it be assumed that an object at point T is to be observed from point P displaced by the amounts Xi, Y1 and Zi with reference to the point O at which a radar antenna is located. The elevation and azimuth angles ibi and 01 of point T with reference to point P can be expressed in terms of the elevation and azimuth angles and 0 of point T with reference to point 0. Likewise, as in the instance previously discussed, the expressions in terms of and 0 for the horizontal and vertical deecting signals Ex and Ey required to produce the desired camera presentation from point P can be derived and are found to be:

In the circuit shown in Figure 7 for generating these signals, a signal which varies proportionally to r during 'an interval following each radar transmitted pulse is developed across condenser 110. ,To generate this signal, negative pulses of the form shown at 111, commencing at time ti corresponding to the transmission of a radar pulse and terminating at time t2 prior to transmission of the next subsequent radar pulse, are supplied to the grid of vacuum tube 112 to render it non-conducting during the interval t1-t2. The time constant of the RC circuit comprising resistor 114 and condenser 110 may be made such that the portion of the signal 113 developed across condenser between times t1 and t2 is essentially linear and therefore proportional to r. This signal is supplied through an isolating amplifier 115 to a tap on circular potentiometer 116. The opposite tap of the potentiometer is grounded through connection 117. The potentiometer is provided with four rectangularly displaced sliders 118, 119, and 121 which are rotated in synchronism with elevation angle Potentiometer 116 is so constructed and operated, similarly to those of Figures 2 and 4 as hereinbefore set forth, that a signal equal to r sin p is developed between sliders 118 and 120, while a signal equal to r cos 95 is developed between sliders 119 and 121. The r sin qs signal is supplied through connections 122 and 123 to the primary winding of a transformer 124.

By means of batteries 125 and 126 and potentiometer 127, whose slider is connected to onel terminal .of the tegrating the modulated signal' and rectifying the insecondary winding of transformer 124, a potential of' magnitude Z1 is subtracted. from the signal in the secondary winding of transformer 124 to vyield,'betweenthe other secondary winding terminal and ground, a signal vequal to r sin Z1. The latter signal is supplied through connection 128, and optionally through a rectifier 129, to the divisor input terminals of dividers 130,131, 132 and 133. The functionof rectifier 129 will be set forth hereinafter.

Ther cos qt signal developed between sliders 119 and 121l of potentiometer 116 is supplied through connections 134 and 135 to the primary winding of transformer 136. v

Transformer 136 is provided with la pair of secondary respectively. Each potentiometer is provided with a pair of opposed sliders which are rotated in synchronism with azimuth angle 9, and the potentiometers are so constructed and Aoperated as to develop, between sliders 139 and 140, a signal-equal tor cos p cos 0, and, between windings, the terminals of each of which are connected.

to oppositely disposed taps on potentiometers- 137 and 138 sliders 141 and 142, a signal equal to r cos 4: sin- 0. By

means of batteries 143'and 144 and potentiometer 145 there is subtracted, from the signal from potentiometer 137, a potential of magnitude X1. Also, by means of a network comprisingA batteries 146 and-147 and resistors 148, 149 and 150,there is added to and subtracted from the resultant signal a further small potential AXi corresponding to one-half the X displacement between thel eyes of the observer. The resultant signals, appearing a't opposite ends of resistor 150, are supplied' through Connectionsl 159 and V160 tothe dividend input terminals of dividers 132 yand 133. These dividers operate to divide the dividend inputs by the divisor inputs to yield horizontal dellecting signals according to the following expressions:

divisor may be accomplished, for example, by producing separate carrier signals respectively amplitude modulated by the 'dividend and by the divisor. carrier signals are heterodyned,I one with the other, and either the sum or diterence term .produced by heterodyning is .selected and rectified to yield a signal which is essentially proportional to the product ofthe two modulating signals. For optimum results under all cir- \cumstances, and particularly when the two signals to be multiplied are not appreciably different in amplitude, it is preferable, in the heterodyning process, to employ a square-law rectifier.

Alternatively the division of the dividend by the divisor signal may bev achieved directly. To this end there may be employed a pentagrid. tube having -a remote cut ol grid and a linear control grid, each being shielded from the other and from the tube plate. The dividend signal is applied to the linear grid, while the. divisor signal is applied to the remote cut ot grid, which is' negatively biased. The tube plate current will be substantially proportional to the ratio of the grid voltages.

It will be understood, of course, that,'with reference to any ofthe foregoing methods, a single-sided arrangey ment may be used if signals of but one polarity are involved, but .thata push-pullarrangement should be emr ployed where either one or bothfof the signals changes polarity.

In the system according to Figure 8, the scanning antenna 170 of radar 171 is assumed to be located at point O. PointP, in accordance with Figure 6, is the virtual viewing point displaced from point 0 in rectangular coordinates by the amounts X1, Y1 and Z1. Camera indications corresponding respectively to -the viewsfrom These are the horizontal deflecting signals needed to v produce the two camera presentations fora stereoscopic presentation with a viewing point P having the coordinates Xi, Y1, Z1.

In a similar manner, by means of batteries 151 and 152 and potentiometer153, there is subtracted from the signal from potentiometer 138 a potential of magnitude Yi. Also, by means of a network comprising batteries 154 and 155 and resistors v156, 157 and 158, there is added to and subtracted from the resultant signal a further small potential AYi corresponding to one-half the Y displacement between the eyes of the observer. The resultant signals, appearing at opposite ends of resistor 158, are supplied through connections 161 and 162 to the dividend input terminals of dividers 130 and 131. These dividers operate to divide the dividend inputs by the divisor inputs to yield vertical dellecting signals according to the following expressions, which are complementary to the horizontal dellecting signals according tol-Equations (7) and (8):

r cos sin -Yl-l-AYl] EVfi r sin Z1 r eos d sin -Yl-AYI E fi' r sin 1a-Z1 The vonage dividers 130, 131, 132 and 133 may faire supplied through connections 174 and 175 respectively points P and P are to be produced. Points P'and P" are displaced in opposite directions with reference to point P by the amounts 'AXi and AYi. It will, of course, be understood that they might likewise be displaced in the Z direction.. I

Elevation and azimuth data (rp and 0) are suppliedl from radar 171 through connection 172 to detiecting signal generator'173, which may be substantially as shown in Figure 7. Horizontal deecting signals Ex and Ex', in accordance with Equations 7 and `8, are

to cathode ray tubes 178 and 179. Likewise vertical dellecting signals Ey and Ey' `in accordance with Equations 9 and l0 are supplied through connections 176 and 177 respectively to cathode ray tubes 178 and 179. Received reected signals from radar 171 are supplied through .connections 184 and 185 to cathode ray tubes 178 and 179, as in the systems previously discussed, to modulate the intensity of -tle electron beams in both tubes. For the reasons hereinbefore set forth, there will be produced, on screens 180 and 181 of cathode ray tubes 178 and 179, camera presentations corresponding to the views from points P' and P of all objects within the field of view of radar 171. These camera presentations may be viewed 'through stereoscopic viewer 182 by an observer whose -eyes are located at 183 and who will thereby obtain the same three-dimensional impression as would be obtained by unimpeded visual observation from point P.

Referring again to Figure 7, which shows the deecting signal generating circuits employed in the system according to Figure 8, rectilier 129 may be so poled that only divisor signals of positive polarity are supplied from connection 128 to the divisor input terminals of dividers These modulated 130, 131, 132 and 133. This is desirable when the virtual viewing point P of Figure 6 is located at a point above the surface of the ground on which the radar is located (e. g. in an aircraft). If, under such circumstances, rectifier 129 is not included in the circuit, divisor signals of positive polarity will be supplied to the divisor input terminals of the dividers for objects above the virtual viewing point, and divisor signals of negative polarity will be supplied for objects below the virtual viewing point. Obviously this would lead to confusion since it would be impossible from the stereoscopic presentation to determine which indications corresponded to objects above the virtual viewing point and which to objects below. By appropriately poling rectiiier 129, divisor signals corresponding either to objects above or below the virtual viewing point may be eliminated and only those objects within a selected hemisphere whose axis parallels the Z axis may be ma'de to appear in the stereoscopic presentation. Obviously switching means may be included to change the polarity of rectier 129 so as to select either the hemisphere above or the hemisphere below the plane through the virtual viewing point perpendicular to the Z axis. Likewise, it would be possible to cause objects in one hemisphere to produce a stereoscopic indication in one color and to cause objects in the opposite hemisphere to appear in the same stereoscopic presentation in another color, thereby providing a convenient means of discrimination between targets in the two hemispheres.

It will, of course, be understood that the invention is susceptible of embodiment in physical'forms other than those here shown and that component circuits other than those described, but adapted to produce equivalent results, may be devised by those skilled in the art based on the principles hereinbefore set forth. Numerous variations in the manner of applying these principles are likewise contemplated, which it is unnecessary to set forth here in detail. Thus, for example, the cathode ray indicators used to produce the-desired camera presentations may make use of deecting elements other than the conventional rectangularly disposed electric dellecting plates.' I n this event the dellecting signals applied will, in general, be of forms different from those herein prescribed. From the foregoing discussion it will be apparent, however, that, from the data supplied by the radar system, appropriate deilecting signals can be derived to meet the requirements for production of the camera presentation regardless of type of indicator employed. Accordingly the scope of the invention is to be regarded as subject only to the limitations imposed by the appended claims.

' I claim:

l. In a radiant energy object position indicating system, a receiver, means including a directional antenna for causing said receiver selectively to receive energy emanating from objects variously disposed in space and having different bearings from said antenna, said directional antenna being controllable to vary its direction of maximum receptivity, said antenna direction being deiined by the elevation angle which the directional axis 'of said antenna forms with a predetermined reference plane and the azimuth angle which the projection of tron beam in response to said received energy, and means for applying said signals to said deflecting elements to produce a visual presentation comprising indications of the energy received from said objects.

2. In a radiantl energy object position indicating syssaid axis upon said reference plane forms with another` tional antenna being controllable to vary its direction of' maximum receptivity, said antenna direction being deiinedby the elevation angle which the directional axis. of said antenna forms with a predetermined reference plane and the azimuth angle which the projection of said axis upon said reference plane forms with another plane normal to said reference plane, means for providing data with respect to the ranges of objects from which said energy is received, means for generating deilecting signals, one of said signals being a function of the cotangent of said elevation angle and the sine of said azimuth angle, the other of said signals being a function of the cotangent of said elevation angle and the cosine of said azimuth angle, and at least one of'said signals being also a function of said range and of the displacement of said antenna from a predetermined point in space, an electron beam indicator having orthogonal deilecting elements, means for controlling the intensity of said electron beam in response to said received energy, and means for applying said signals to said deccting elements toproduce a visual presentation comprising indications of the energy received from said objects.

3. In an object position indicating system, a directional receiver whose direction of maximum receptivity is variable, said direction being defined jointly by the elevation angle which said direction forms with a predetermined reference plane and the azimuth angle which the projectionl of said direction upon said reference plane i forms with another plane normal to said reference plane, an indicator comprising a bidimensional presentation delvice and responsive to energy received by said receiver to produce visible indications upon said presentation device, said indicator also beingv controllable to vary the positions of said indications upon said presentation device, means for deriving detlecting signals which are functions of said elevation and said azimuth angles of said direction of maximum receptivity, and means for controlling said indicator in response to said deilecting signals to displace said indications in one of two mutually perpendicular directions by an amount substantially proportional to the product of the cotangent of said elevation angle and the sine of said azimuth angle, and further to displace said indications in the other of said perpendicular directions substantially proportionally to the product of the cotangent of said angle of elevation and the cosine of said angle of azimuth.

4. In an object position indicating system, a directional receiver whose direction of maximum receptivity is variable, said directionbeing defined jointly by the elevation angle which said direction forms with a predetermined reference plane and by the azimuth angle which the projection of said direction upon said reference plane forms with a second plane normal to said reference plane, an indicator comprising a bidimensional presentation device and responsive to energy received by said receiver to produce visible indications upon said presentation device upon the reception of energy by said receiver, said indicator being controllable to vary the positions of said indications with respect to said presentation device, means l to the cotangent of said angle of elevation and angularly substantially proportionally `to said azimuth angle.

5. In a stereoscopic object position indicating system,

a receiver, a pair of directional antennae whose directions of maximum receptivity are variable, said directions being dened by the elevation angles which the directional axes of said antennae form with a predetermined reference plane and by the azimuth angles which the projections of said directional axes upon said reference plane form with a second plane normal 'to said reference plane, an indicator comprising a pair of bidimensional Apresentation devices and responsive to energy received by said receiver to produce indications on said presentation devices, said indicator being controllable to vary the positions of said indications withv respect AtoV said presentation devices, means for deriving two sets of delecting signals, cach of which is a function of the elevation and azimuth angle of one of said directional axes, means for controlling said indicator in response to said detlecting signals to displace said indications upon each -of said presentation devices in one of two mutually perpendicular directions substantially proportionally to the product of the cotangent of said angle of elevation and the cosine of said azimuth angle of one of said directional axes, and in the other of said mutually perpendicular directions substantially proportionally to the product of the cotangent of said 1 angle of elevation andthe sine. of said azimuth-angle of said last-named directional axis, and stereoscopic viewing means for viewing said pair of presentation devices.

6. In a radiant energy object position indicating system, a receiver, means including a directional antenna for causing said receiver selectively to receive energy emanating from objects variously disposed in space, said antenna direction being defined by the angle which the directional axis of said antenna forms with a predetermined reference plane and the azimuth anglewhich the projection of said axis upon said reference plane forms with another plane normal to said reference plane, an indicator comprising a source of an electron beam and beam-detiecting means, means for controlling the intensity of said electron beam in response to said received energy, means for deriving signals indicative of said elevation and said azimuth angles of said antenna direction, and means for applying said signals to said beam-dellecting means to deect said beem in one of two mutually perpendicular directions substantially proportionally to the product of .the cotangent of said elevation angle' and the sineof said. azimuth angle, and in the other of saidtwo mutually perpendicular directions substantially proportionally to the product of the cotangent of said elevation angle and the cosine of said azimuth angle. y

7. In an object position indicating system, a directional receiver whose direction of maximum receptivity is vari able, said direction being defined jointly by the elevation angle which said direction forms with a predetermined reference plane and the azimuth angle which the projection of said direction upon said reference plane forms with another plane normal to said reference plane, an indicator comprising a source of an electron beam anda bidimensional presentation device upon which said electron beam is adapted to impinge, said indicator being supplied with received signals from said receiver and being responsive thereto to produce indications of the reception of energy by said receiver, said indicator also comprising means responsive to signals supplied thereto controlledly forms with another plane normal to said reference plane, an indicator comprising a source of an electron beam and a bidimensional presentation device, said indicator being responsive to energy received by said receiver from objects in space to produce visible indications on said presentation device, said indicator also comprising means -for controlledly deecting said beam to vary the positions of said indications, means for deriving deecting signals which are functions o f said azimuth and said elevation angles of said direction of maximum'recept'ivity of said receiver, means for 'supplying said deecting signals to said beam-deecting means to dcect said beam in one of two mutually perpendicular coordinate directions substantially proportionally to the product of the cosine of said azimuth angle and the cotangent of said elevation `angle of said direction of maximum receptivity and inthe other of said mutually perpendicular coordinate directions substantially proportionally tothe product of the sine of said azimuth angle and the cotangent of said ele\- vation angle, means for deriving signals representative of the projection of said direction upon said referenceplane forms with -another plane normal to said reference plane, said receiver being controllable to vary said direction7 of maximum receptivity so as to elect scanning of a plurality of points in a predetermined region of space, means responsive to variations in said direction ofmaximum receptivity of said receiver for -producing dcecting signals which are functions of the elevation and azimuth angles of said scanned points, with respect to an arbitrarily-locatedA reference point in space, as measured with reference to said two mutually perpendicular planes, an indicator comprising a bidimensional presentation device and a source of an electron beam, and responsive to energy received by said receiver from objects located within said predetermined region of space to produce indications on said presentation device, said indicator being controllable to vary the position of said beam to elect displacement of said indications, and .means responsive to said deecting signals for controlling said indicator to displace said beam in one of two mutually perpendicular coordinate directions to detiect said beam thereby to alter the positions of said I indications upon said presentation device, means for deriving a signal substantially proportional to the product of the cotangent of the angle of elevation and the sine of the angle of azimuth of said direction of maximum receptivity, means for deriving a signal substantially pro-v portional to the product of the cotangent of said angle of elevation and the cosine of said angle of azimuth, and means for supplying said last-named two signals to said beam-dellecting means to deliect said beam and to control the positions of said indications upon said presentation device. f @l 8. In an object position indicating system, a receiver of variably directional receptivity, the direction of maximum receptivity of said receiver being detined by the elevation angle which said direction forms with a predetermined reference plane and the azimuth angle which the projection of said direction upon said reference plane substantially proportionally to the productvof the cotangent of said angle of elevation of said scanned points with respect to said arbitrarily-located reference point and the cosine of said azimuth angle of said scanned points i with respect to said reference point, and in the other of said two mutually perpendicular coordinate directions substantially proportionally to the product of said cotangent of said last-named elevation angle and the sine of said last-named azimuth angle.

l0. In anobject position indicating system, a receiver comprising a directional antenna whose directional axis is orientable abouta predetermined point in space, the direction of said antenna being deined by the elevation angle' which said directional axis forms with a predetermined reference plane and the azimuth angle which the projection of said directional axis uponv said reference plane l forms with another plane norm'al to said reference plane,

' an indicator comprising a bidimensional presentation device and a source of an electron beam for producing visible indications on said presentation device upon the reception by said receiver of energy emanating from objects in space, said indicator also being controllable to deect saidbeam thereby to displace said indications, means for controlling said receiver and said antenna to effect a scanning of a plurality of points lying within aL pre'- determined region of space, means for deriving signals indicative of the ranges of said scanned points, and means responsive to orientational motion of said directional axis, to said received energy, and to said range signals for providing indications upon said presentation device whose geometric interrelationships simulate those of a photographic image of said objects taken from an arbitrarilylocated point displaced from said point of orientation of said antenna, said last-named means comprising means for controlling said indicator to displace said indications in each of two mutually perpendicular coordinate directions substantially proportionally to the fractions:

respectively, where r is the range of an object fromwhich energy is received, is said elevation angle, 0 1s sald azimuth angle, and X1 and Y1 are the horizontal coordinate displacements and Z1 is the vertical coordinate displacement of said arbitrarily-locatedpoint from sald predetermined point of orientation of said antenna.

l1. A system in accordance with claim 10, comprising, in addition, means for producing other indications of said objects upon said indicator which are displaced in one of said two mutually perpendicular directions substantially proportionally to the product of the cotangent of said angle of elevation and the cosine of said angle of azimuth, and in the other of said mutually perpendicular directions substantially proportionally to the product of the cotangent of said angle of elevation and the'sine of said angle of azimuth, and stereoscopic viewing means for enabling the stereoscopic viewing of said first-named indications by one eye of an observer and of said other ingications by another eye of said observer.

l2. In an object position indicating system, a receiver,

means including a directional antenna for causing said of the directions of said objects from a predetermined reference point displaced from said antenna location, an indicator supplied with said modified signals and with vsaid received energy-for producing a bidimensional presentation comprising indications of the directions of said objects from said predetermined reference point, and a' \uni1aterally conductive signal transfer device included in said signal modifying meansvand responsive only to signals of predetermined polarity. for preventing the presentation at said indicator of indications of the bearings of objects located exterior to a predetermined hemisphere, one of whose boundaries is a plane including said reference point. A

References Cited inthe le of this patent UNITED STATES PATENTS 2,151,549 Becker Mar. 21, 1939 .2,408,050 De Rosa Sept. 24, 1946 2,409,462 Zworykin Oct. 15, 1946Y 2,419,567 Labin Apr. 29, 1947 2,426,189 Espenschied Aug. 26, 1947 2,426,979 l Ayres Sept. 9, 1947 2,428,351 Ayres Oct. 7, 1947 2,449,542 Ayres et al Sept. 21, 1948 

